I would mount the antenna near the back of the truck bed, so you reduce reflection off the cab. Also, if you run an amp, you really don't want RF that close to you or your passengers.I think there are stake hole mounts that you can put in under a tonneau cover, that extend out the side a bit.
I ran a Ram 1500 with a 2950 and a Wilson 5' Silverload on a stake hole mount for several years and had good success with it. Locally, it did well, and back in 2000 with the solar cycle being active, I worked Europe almost everyday from the mobile.
I remember having a 20 minute QSO with a guy from Amsterdam while driving someplace one day.
I always recommend grounding, or bonding, as much as you can to reduce noise. Run ground straps from the truck bed and cab to the frame, run ground straps from exhaust clamps to the frame, run ground straps from the antenna mount to the frame, and so on and so on.